1. Technical Field
The invention relates to a control system incorporated into machinery such as power operated meat skinning equipment, a power driven band saw or the like, to detect the touch of a bare or gloved human hand upon a conductive surface such as a rotating blade or a rotating feed mechanism, in order to provide automated means for protective action against harm to an operator by immediately disconnecting the power drive means from the rotating element, stopping the rotating element and then reversing the direction of rotation of the rotating element.
2. Background Information
Various types of tools have been devised for performing various operations such as power actuated drills, grinders, meat cutting and trimming tools, etc. which are operated by power drive means, such as a chain or belt drive, from the output shaft of an electric motor.
One type of such a machine which is used in the meat industry is referred to as a meat skinning machine. These machines may be floor mounted units having a horizontally extending rotatable shaft on which is mounted a plurality of teeth located adjacent a skinning knife blade. An operator holds a piece of meat, such as a ham, and presses the meat against the rotating teeth which in combination with the blade, removes the skin from the meat. Another type of equipment used in the meat industry and in other types of industry is a power driven band saw.
As with any power operated equipment there is always the danger that the hands or fingers of an operator will come into contact with the rotating blade of the band saw, or the rotating toothed feed shaft and adjacent cutting blade of a skinning machine Therefore to ensure safety to the operator when operating such equipment, he or she will usually wear protective metal mesh gloves of the type shown in U.S. Pat. Nos. 4,384,449, 4,470,251 and 4,004,295. These gloves usually consist of a fine metal mesh covered with strands of a synthetic fiber. The metal mesh prevents or reduces the cutting of the operator upon contacting a cutting blade. Although these metal mesh gloves provide good protection to the operator and have been found to be quite satisfactory for reducing injury to the operator, as a result of non mechanical injuries. They are not suitable for many types of mechanical cutting operations. As a result, it is still desirable to provide even greater protection to the operator in certain applications by providing a system which instantaneously removes the power drive source from the rotating element upon contact of the operator's gloved hand with the element or certain other areas of the particular equipment being used by the operator.
Examples of other protective devices and systems for use in reducing injury to the operator as shown in U.S. Pat. No. 941,726, 3,785,230, 4,026,177, 4,391,358, and 4,621,300. Still other types of protective devices provide a mechanism attached to the hands of the operator which automatically pull the operator's hand away from the dangerous part of the equipment upon a certain event occurring. Examples of such safety equipment are shown in U.S. Pat. Nos. 2,978,084; 3,011,610; 3,047,116; 4,195,722; and 4,321,841.
Still another type of safety control system is shown in German Patent application Serial No. DE 35 01 021. Although the safety control system of this German device may be satisfactory for certain applications, even after contact of the two electrically isolated components and immediate deenergizing of the electric, there will be some continued movement of the rotating cutting blade or feed roller due to inertia which may continue to draw the operator's gloved hand into the machine possibly causing significant injury. Another problem with this German device is that the machine can be energized and operated without the operator wearing the gloves since energization of the machine does not require the electrical control circuit to first sense the presence of the operator wearing the metal gloves.
Many of the disadvantages in existing safety control systems intended for use with equipment as of the general type of the present invention, are believed overcome by the control system of U.S. Pat. No. 4,965,909. In this system a reversible electric motor is utilized which automatically reverses upon contact between one of the operator's metal gloves and the rotating metal component, to prevent the operator's hand from being drawn into the cutting element by the inertia of the rotating element. Although the use of such a reversible electric motor provides increased safety to the system, it requires a relatively expensive motor and reversing mechanism. Also it is desirable to reduce the system reaction time even further, since significant time is required for the electrical and mechanical components necessary for motor reversal to change their status, thus applying reverse current to the motor and overcoming the back emf for motor reversal, even though these times are measured in milliseconds.
Therefore, the need exists for an improved safety control system which immediately disconnects the power drive source from a rotating metal component of a meat processing machine or other power driven equipment, and which stops and then causes reversal of the rotating component to prevent injury to the operator upon an electric conductive metal protective glove worn by the operator or operator's bare skin contacting a particular metal component.